Cermets are refractories which include a ceramic component and a metal component. Examples of cermets include metal and ceramic carbides, such as: titanium carbide (TiC), molybdenum (Mo) and nickel (Ni); tungsten carbide (WC) and cobalt (Co); and tungsten carbide (WC) and nickel (Ni). Typically, cermets have properties which neither the ceramic component nor the metal component exhibit alone.
One method of forming cermets includes disposing a solid-phase metal on top of a porous ceramic compact. The solid-phase metal is then heated to a temperature above its melting point to cause the metal to become molten. The molten metal infiltrates the pores in the porous ceramic compact and forms a cermet upon cooling.
Often, however, the metal component includes metal oxides which are present as impurities. These impurities can form a metal oxide layer surrounding the molten metal during melting which prevents infiltration of the porous ceramic compact. Alternatively, metal oxides can form in situ by reaction of the metal component with oxygen in the surrounding atmosphere during melting of the metal component.
In one technique to overcome this problem, the porous ceramic compact and molten metal are exposed to a pressure which is significantly higher or lower than atmospheric pressure. However, exposure of the porous ceramic compact and metal to such pressures at temperatures sufficient to melt the metal often requires the use of specialized furnaces which limit mass production of cermets to batch-type processing, as opposed to continuous-type processing. Further, the location of rupture of the metal oxide layer at the molten metal generally cannot be predetermined, thereby limiting control of infiltration by the metal after the metal oxide layer has ruptured.
A need exists, therefore, for a method of infiltrating molten metal into a porous ceramic compact to form a cermet which overcomes or minimizes the above-mentioned problems.